EP0885446A1 - Multilayer capacitor - Google Patents
Multilayer capacitorInfo
- Publication number
- EP0885446A1 EP0885446A1 EP97943117A EP97943117A EP0885446A1 EP 0885446 A1 EP0885446 A1 EP 0885446A1 EP 97943117 A EP97943117 A EP 97943117A EP 97943117 A EP97943117 A EP 97943117A EP 0885446 A1 EP0885446 A1 EP 0885446A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- palladium
- ceramic
- electrode layers
- multilayer
- copper oxide
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 239000003990 capacitor Substances 0.000 title claims abstract description 54
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims abstract description 42
- 239000000919 ceramic Substances 0.000 claims abstract description 41
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 claims abstract description 28
- 239000005751 Copper oxide Substances 0.000 claims abstract description 28
- 229910000431 copper oxide Inorganic materials 0.000 claims abstract description 28
- 229910052763 palladium Inorganic materials 0.000 claims abstract description 14
- SWELZOZIOHGSPA-UHFFFAOYSA-N palladium silver Chemical compound [Pd].[Ag] SWELZOZIOHGSPA-UHFFFAOYSA-N 0.000 claims abstract description 12
- 238000004519 manufacturing process Methods 0.000 claims abstract description 11
- 238000000034 method Methods 0.000 claims abstract description 11
- 229910002113 barium titanate Inorganic materials 0.000 claims abstract description 10
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims abstract description 7
- JRPBQTZRNDNNOP-UHFFFAOYSA-N barium titanate Chemical compound [Ba+2].[Ba+2].[O-][Ti]([O-])([O-])[O-] JRPBQTZRNDNNOP-UHFFFAOYSA-N 0.000 claims abstract description 6
- 229910003445 palladium oxide Inorganic materials 0.000 claims abstract description 6
- 229910000108 silver(I,III) oxide Inorganic materials 0.000 claims abstract description 6
- 229910001252 Pd alloy Inorganic materials 0.000 claims abstract description 5
- 239000011888 foil Substances 0.000 claims description 15
- 239000000203 mixture Substances 0.000 claims description 9
- 238000007650 screen-printing Methods 0.000 claims description 6
- 239000000463 material Substances 0.000 claims description 5
- 238000005245 sintering Methods 0.000 claims description 4
- 238000001354 calcination Methods 0.000 claims description 2
- 239000007772 electrode material Substances 0.000 abstract description 3
- 229920002134 Carboxymethyl cellulose Polymers 0.000 abstract 1
- 235000010948 carboxy methyl cellulose Nutrition 0.000 abstract 1
- 229920006184 cellulose methylcellulose Polymers 0.000 abstract 1
- 239000011153 ceramic matrix composite Substances 0.000 abstract 1
- 238000012710 chemistry, manufacturing and control Methods 0.000 abstract 1
- 239000010410 layer Substances 0.000 description 42
- 229960004643 cupric oxide Drugs 0.000 description 19
- 239000000843 powder Substances 0.000 description 11
- 230000000694 effects Effects 0.000 description 4
- 239000010936 titanium Substances 0.000 description 4
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 3
- 229910052788 barium Inorganic materials 0.000 description 3
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 3
- 239000011230 binding agent Substances 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 239000011343 solid material Substances 0.000 description 3
- 238000007669 thermal treatment Methods 0.000 description 3
- 229910052719 titanium Inorganic materials 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 230000002411 adverse Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000011575 calcium Substances 0.000 description 2
- 229910010293 ceramic material Inorganic materials 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 230000032798 delamination Effects 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000011241 protective layer Substances 0.000 description 2
- 229910052709 silver Inorganic materials 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- 229910052688 Gadolinium Inorganic materials 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- 229910005887 NiSn Inorganic materials 0.000 description 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 1
- 239000002270 dispersing agent Substances 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- UIWYJDYFSGRHKR-UHFFFAOYSA-N gadolinium atom Chemical compound [Gd] UIWYJDYFSGRHKR-UHFFFAOYSA-N 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000000386 microscopy Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- QEFYFXOXNSNQGX-UHFFFAOYSA-N neodymium atom Chemical compound [Nd] QEFYFXOXNSNQGX-UHFFFAOYSA-N 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 239000010944 silver (metal) Substances 0.000 description 1
- 238000005476 soldering Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 229910052712 strontium Inorganic materials 0.000 description 1
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 238000011179 visual inspection Methods 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G4/00—Fixed capacitors; Processes of their manufacture
- H01G4/002—Details
- H01G4/005—Electrodes
- H01G4/008—Selection of materials
- H01G4/0085—Fried electrodes
Definitions
- the invention relates to a ceramic multilayer capacitor comprising a number of ceramic layers on the basis of barium titanate as well as a number of electrode layers of palladium or a silver-palladium alloy, the ceramic layers and the electrode layers being alternately stacked to form a multilayer, which is also provided with two external electric connections which are in contact with a number of said electrode layers.
- the invention also relates to a method of manufacturing this ceramic multilayer capacitor.
- barium titanate on the basis of barium titanate
- the barium sites and the titanium sites of the material may be substituted with further suitable donor ions and/or acceptor ions, such as Mn, Bi, Nb etc. Such substitutions of barium and/or titanium are important to provide the ceramic material with properties which are necessary for the intended field of application of the capacitors.
- Ceramic multilayer capacitors of the type mentioned in the opening paragraph as well as methods of manufacturing said capacitors are known, for example, from United States Patent Specification US 4,882,651.
- a description is given, more particularly, of a CMC which is provided with cover layers of a ceramic material.
- the chemical composition of the cover layers is identical to that of the ceramic layers situated between the electrode layers.
- cover layers whose grain size is larger than that of the ceramic layers.
- CMCs have an important drawback. Particularly in the case of capacitors comprising a large number of electrode layers (20 or more), the internal mechanical strength leaves much to be desired. Under specific conditions, this may cause delamination in the capacitor, leading to cracks between the electrode layers and the ceramic layers. This adverse effect takes place, in particular, if these capacitors are subjected to a thermal treatment. Such a thermal treatment occurs, for example, during soldering of the capacitors.
- the invention more particularly aims at providing a CMC in which said delamination is reduced so that the internal mechanical strength is increased.
- the CMC in accordance with the invention should also exhibit a long service life.
- the invention additionally aims at providing a method of manufacturing CMCs having a higher internal mechanical strength and a long service life.
- a CMC which is characterized in that the electrode layers comprise copper oxide.
- a preferred embodiment of the CMC in accordance with the invention is characterized in that the quantity of copper oxide in the palladium or the silver-palladium alloy of the electrode layers ranges from 0.5 to 15 wt. %, calculated with respect to the overall quantity of palladium, silver and copper oxide.
- the effect of the invention occurs to an insufficient degree.
- the use of a quantity of copper oxide in excess of 15 wt. % leads to a substantial reduction of the electric conductivity of the electrode layers.
- a good compromise between both adverse effects is achieved if the above-mentioned copper-oxide content ranges between 1 and 10 wt. % .
- Optimum results as regards service life and mechanical strength are achieved if the copper- oxide content ranges between 4 and 6 wt. % .
- Another interesting embodiment of the ceramic multilayer capacitor is characterized in that the thickness of the electrode layers ranges between 0.7 micron and 2.0 microns.
- the layer thickness of capacitors in accordance with the invention is approximately 1.0 micron.
- the invention also relates to a method of manufacturing a ceramic multilayer capacitor, which method comprises the following steps: screen-printing of electrode layers on a ceramic foil using a palladium or a silver-palladium paste, stacking a number of these foils to form a multilayer, compressing the multilayer, - subdividing the multilayer into individual multilayer elements, calcining and sintering of the multilayer elements, providing electric connections at one or more side faces of the multilayer elements.
- This method is characterized in accordance with the invention in that the palladium paste or the silver-palladium paste contains copper oxide, and sintering is carried out at a maximum temperature in the range between 1180 and 1220 °C.
- Multilayer capacitors manufactured in accordance with the inventive method are substantially less subject to crack formation and exhibit a relatively long service life.
- the palladium paste or the silver-palladium paste contains a quantity of copper oxide in the range from 0.5 to 15 wt. %, calculated with respect to the overall quantity of palladium, silver and copper oxide.
- said quantity of copper oxide ranges between 1 and 10 wt. %, and more preferably between 4 and 6 wt. %.
- the thickness of the electrode layers manufactured by means of said silver-palladium paste preferably ranges between 0.7 micron and 2.0 microns.
- Fig. 1 is a schematic, sectional view of a multilayer capacitor in accordance with the invention
- Fig. 2 graphically shows the results of accelerated life tests to which (a) capacitors in accordance with the invention and (b) capacitors not in accordance with the invention are subjected.
- Fig. 1 shows a multilayer capacitor in accordance with the invention.
- This multilayer capacitor comprises a number of ceramic layers 1 on the basis of doped barium titanate (BaTiO 3 ).
- the exact composition is
- Said capacitor additionally comprises a number of electrode layers 2 which predominantly comprise Ag-Pd with 5 wt. % copper oxide, calculated with respect to the overall quantity of palladium, silver and copper oxide.
- the capacitor also comprises two electric connections 3 which are provided on two opposite side faces of the capacitor. These connections contain a solderable material, for example copper.
- the electrode layers are provided on a ceramic foil by means of screen printing, whereafter a number of said printed foils are stacked. As shown in Fig. 1, the ceramic foils are stacked in such a manner that successive electrode layers are alternately connected to one of the two electric connections.
- ceramic multilayer capacitors demonstrating the effect of the invention comprise at least twenty, and preferably at least hundred, electrode layers.
- the thickness of said electrode layers typically ranges from approximately 0.7 to 2.0 micrometers.
- the ceramic foils have a typical thickness in the range from 5 to 20 micrometers.
- the capacitors are provided with a protective layer 4 on the upper side and the lower side of the stacked, printed foils.
- Said protective layer generally consists of a number of unprinted ceramic foils which are stacked together with the printed ceramic foils.
- the ceramic multilayer capacitors in accordance with the invention are manufactured as follows. First, a powder mixture is prepared by mixing powders of oxides and/or carbonates of the desired metals in quantities corresponding to the intended composition. This powder mixture is suspended in an aqueous solution to which a small quantity of a dispersing agent is added. The suspension is ground for several hours in a continuous attrition mill, so that the average particle size of the powder particles is reduced to below 0.4 micrometer. Subsequently, the powder is dried. Next, the dried powder is calcined in air for several hours at approximately 1100 °C. In this process, the desired, doped BaTiO 3 is formed. Subsequently, said BaTiO 3 is ground for several hours.
- the resultant powder has an average particle size below 1.0 micrometer.
- a binder solution is added to this powder.
- green ceramic foils having a thickness, for example, of 40 micrometers are drawn from the powder/binder mixture.
- a large number of electrode layers are screen-printed onto these foils.
- a screen-printing paste comprising approximately 40 wt. % of a binder solution (solvents and polymers) and approximately 60 wt. % of a solid material.
- Said solid material contains approximately 15 wt. % of a ceramic powder whose composition corresponds to that of the ceramic layers.
- the solid material contains approximately 85 wt.
- the layer thickness of the unsintered electrode layers is approximately 1.4 microns.
- a number of the foils on which electrode layers have been printed and which have desired dimensions are stacked. The stacking process is carried out in such a manner that the electrode layers of the even layers and the electrode layers of the odd layers are slightly displaced relative to each other.
- the stacked foils are uniaxially compressed under a high pressure (approximately 300 bar) and at an elevated temperature (approximately 80 °C) to form a multilayer structure.
- This structure is subsequently broken in one direction to form rods and in a second direction (at right angles to the first direction) to form individual multilayer capacitor elements.
- These elements are, in succession, calcined and sintered (maximum temperature 1180-1220 °C) in air.
- the multilayer capacitor elements are provided, on two facing surfaces, with electric connections of copper by means of immersion copperplating. These connections are galvanically reinforced and provided with a solderable NiSn alloy. Subsequently, the mechanical and electrical properties of the resultant ceramic multilayer capacitors can be measured.
- a first number of ceramic multilayer capacitors (b series) was manufactured on the basis of the above-mentioned doped BaTiO 3 .
- the Ag-Pd screen-printing paste used in said b-series did not contain copper oxide.
- a second number of ceramic multilayer capacitors (a-series) was manufactured.
- the screen-printing paste used for said second series contained approximately 5 wt. % copper oxide, calculated with respect to the overall quantity of Ag, Pd and copper oxide. Both series were tested for mechanical strength and service life.
- Fig. 2 shows the results of accelerated life tests (140 °C, 400 V, DC) for maximally 100 hours.
- the resistance R (ohm) is plotted as a function of time T (hours), the time scale exhibiting a logarithmic variation.
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Ceramic Capacitors (AREA)
- Fixed Capacitors And Capacitor Manufacturing Machines (AREA)
Abstract
The invention relates to a ceramic multilayer capacitor and to the manufacture of same. The capacitor comprises a number of ceramic layers on the basis of barium titanate as well as a number of electrode layers of palladium or a silver-palladium alloy, the ceramic layers and the electrode layers being alternately stacked to form a multilayer, which is also provided with two external electric connections which are in contact with a number of said electrode layers. In accordance with the invention, the electrode layers contain copper oxide, preferably 0.5-15 wt.%, calculated with respect to the overall quantity of palladium, silver and copper oxide. It has been found that the presence of a relatively small, yet effective quantity of copper oxide in the electrode material of Pd or Pd-Ag leads to a considerable increase of the internal mechanical strength and of the service life of CMCs. By employing the method in accordance with the invention, the percentage of rejects in the production of the capacitors can be reduced considerably.
Description
Multilayer capacitor.
The invention relates to a ceramic multilayer capacitor comprising a number of ceramic layers on the basis of barium titanate as well as a number of electrode layers of palladium or a silver-palladium alloy, the ceramic layers and the electrode layers being alternately stacked to form a multilayer, which is also provided with two external electric connections which are in contact with a number of said electrode layers. The invention also relates to a method of manufacturing this ceramic multilayer capacitor.
It is noted that the expression "on the basis of barium titanate" is to be understood to include, apart from pure barium titanate, materials in which the barium content is partly replaced by calcium, strontium or lead and/or by rare earth elements such as gadolinium and/or neodymium, and in which the titanium content is partly replaced by zirconium. In addition, the barium sites and the titanium sites of the material may be substituted with further suitable donor ions and/or acceptor ions, such as Mn, Bi, Nb etc. Such substitutions of barium and/or titanium are important to provide the ceramic material with properties which are necessary for the intended field of application of the capacitors. Ceramic multilayer capacitors (CMCs) of the type mentioned in the opening paragraph as well as methods of manufacturing said capacitors are known, for example, from United States Patent Specification US 4,882,651. In said Patent Specification, a description is given, more particularly, of a CMC which is provided with cover layers of a ceramic material. The chemical composition of the cover layers is identical to that of the ceramic layers situated between the electrode layers. In the known capacitors, use is made of cover layers whose grain size is larger than that of the ceramic layers.
It has been found that the known CMCs have an important drawback. Particularly in the case of capacitors comprising a large number of electrode layers (20 or more), the internal mechanical strength leaves much to be desired. Under specific conditions, this may cause delamination in the capacitor, leading to cracks between the electrode layers and the ceramic layers. This adverse effect takes place, in particular, if these capacitors are subjected to a thermal treatment. Such a thermal treatment occurs, for example, during soldering of the capacitors.
It is an object of the invention to reduce the above-mentioned drawback.
The invention more particularly aims at providing a CMC in which said delamination is reduced so that the internal mechanical strength is increased. The CMC in accordance with the invention should also exhibit a long service life. The invention additionally aims at providing a method of manufacturing CMCs having a higher internal mechanical strength and a long service life.
These and other objects of the invention are achieved by a CMC, which is characterized in that the electrode layers comprise copper oxide.
It has been found that the presence of a relatively small, yet effective quantity of copper oxide in the electrode material of Pd or of Pd-Ag leads to a considerable increase of the internal mechanical strength as well as of the service life of the CMC in accordance with the invention. The working principle of the invention is not exactly known. Tests have shown that by employing the invention, the number of rejects in the production of capacitors can be reduced by a factor of 10 while the service life of the capacitors is increased considerably. A preferred embodiment of the CMC in accordance with the invention is characterized in that the quantity of copper oxide in the palladium or the silver-palladium alloy of the electrode layers ranges from 0.5 to 15 wt. %, calculated with respect to the overall quantity of palladium, silver and copper oxide. If the quantity of copper oxide used is below 0.5 wt. % , the effect of the invention occurs to an insufficient degree. The use of a quantity of copper oxide in excess of 15 wt. % leads to a substantial reduction of the electric conductivity of the electrode layers. A good compromise between both adverse effects is achieved if the above-mentioned copper-oxide content ranges between 1 and 10 wt. % . Optimum results as regards service life and mechanical strength are achieved if the copper- oxide content ranges between 4 and 6 wt. % . Another interesting embodiment of the ceramic multilayer capacitor is characterized in that the thickness of the electrode layers ranges between 0.7 micron and 2.0 microns. If the layer thickness is below 0.7 micron, the electric conductivity of the electrode layers is insufficient. If the layer thickness exceeds 2.0 microns, the capacitance per unit of volume of the capacitor becomes too small. An optimum compromise between both disadvantages is achieved if the layer thickness of capacitors in accordance with the invention is approximately 1.0 micron.
Satisfactory results are attained by means of an embodiment of the capacitor in accordance with the invention, which is characterized in that the composition of the main phase of the material of the ceramic layers corresponds to the formula
[Barj .25 Sro .02 Cao .05 Ndo .30 Gdo .20 xo.i8l[T .ooo]°3' wherein X indicates the number of vacancies in the Ba sites. Experiments have shown that capacitors comprising this type of ceramic layers exhibit a long service life and a low degree of crack formation.
The invention also relates to a method of manufacturing a ceramic multilayer capacitor, which method comprises the following steps: screen-printing of electrode layers on a ceramic foil using a palladium or a silver-palladium paste, stacking a number of these foils to form a multilayer, compressing the multilayer, - subdividing the multilayer into individual multilayer elements, calcining and sintering of the multilayer elements, providing electric connections at one or more side faces of the multilayer elements.
This method is characterized in accordance with the invention in that the palladium paste or the silver-palladium paste contains copper oxide, and sintering is carried out at a maximum temperature in the range between 1180 and 1220 °C. Multilayer capacitors manufactured in accordance with the inventive method are substantially less subject to crack formation and exhibit a relatively long service life.
An interesting embodiment of the method in accordance with the invention is characterized in that the palladium paste or the silver-palladium paste contains a quantity of copper oxide in the range from 0.5 to 15 wt. %, calculated with respect to the overall quantity of palladium, silver and copper oxide. Preferably, said quantity of copper oxide ranges between 1 and 10 wt. %, and more preferably between 4 and 6 wt. %. The thickness of the electrode layers manufactured by means of said silver-palladium paste preferably ranges between 0.7 micron and 2.0 microns.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
In the drawings:
Fig. 1 is a schematic, sectional view of a multilayer capacitor in accordance with the invention,
Fig. 2 graphically shows the results of accelerated life tests to which (a) capacitors in accordance with the invention and (b) capacitors not in accordance with the
invention are subjected.
It is noted that, for clarity, the Figures are not drawn to scale. Fig. 1 shows a multilayer capacitor in accordance with the invention. This multilayer capacitor comprises a number of ceramic layers 1 on the basis of doped barium titanate (BaTiO3). The exact composition is
[BaQ 25 r0 02Cao 05Nd0 30Gd0 20X0 18][Ti1 000]O3. Said capacitor additionally comprises a number of electrode layers 2 which predominantly comprise Ag-Pd with 5 wt. % copper oxide, calculated with respect to the overall quantity of palladium, silver and copper oxide. The capacitor also comprises two electric connections 3 which are provided on two opposite side faces of the capacitor. These connections contain a solderable material, for example copper. In practice, the electrode layers are provided on a ceramic foil by means of screen printing, whereafter a number of said printed foils are stacked. As shown in Fig. 1, the ceramic foils are stacked in such a manner that successive electrode layers are alternately connected to one of the two electric connections. For clarity, only 6 electrode layers are shown in Fig. 1. In practice, ceramic multilayer capacitors demonstrating the effect of the invention comprise at least twenty, and preferably at least hundred, electrode layers. The thickness of said electrode layers typically ranges from approximately 0.7 to 2.0 micrometers. The ceramic foils have a typical thickness in the range from 5 to 20 micrometers. In practice, the capacitors are provided with a protective layer 4 on the upper side and the lower side of the stacked, printed foils. Said protective layer generally consists of a number of unprinted ceramic foils which are stacked together with the printed ceramic foils.
The ceramic multilayer capacitors in accordance with the invention are manufactured as follows. First, a powder mixture is prepared by mixing powders of oxides and/or carbonates of the desired metals in quantities corresponding to the intended composition. This powder mixture is suspended in an aqueous solution to which a small quantity of a dispersing agent is added. The suspension is ground for several hours in a continuous attrition mill, so that the average particle size of the powder particles is reduced to below 0.4 micrometer. Subsequently, the powder is dried. Next, the dried powder is calcined in air for several hours at approximately 1100 °C. In this process, the desired, doped BaTiO3 is formed. Subsequently, said BaTiO3 is ground for several hours. The resultant powder has an average particle size below 1.0 micrometer. A binder solution is added to this powder. Next, green ceramic foils having a thickness, for example, of 40 micrometers are drawn from the powder/binder
mixture. By means of a technique which is known per se, a large number of electrode layers are screen-printed onto these foils. For this purpose, use is made of a screen-printing paste comprising approximately 40 wt. % of a binder solution (solvents and polymers) and approximately 60 wt. % of a solid material. Said solid material contains approximately 15 wt. % of a ceramic powder whose composition corresponds to that of the ceramic layers. The solid material contains approximately 85 wt. % of a finely dispersed powder comprising palladium (70-90 wt. %, preferably 80 wt. %), silver (10-20 wt. %, preferably 15 wt. %) and copper oxide (1-10 wt. %, preferably 4-6 wt. %). The layer thickness of the unsintered electrode layers is approximately 1.4 microns. Subsequently, a number of the foils on which electrode layers have been printed and which have desired dimensions are stacked. The stacking process is carried out in such a manner that the electrode layers of the even layers and the electrode layers of the odd layers are slightly displaced relative to each other. The stacked foils are uniaxially compressed under a high pressure (approximately 300 bar) and at an elevated temperature (approximately 80 °C) to form a multilayer structure. This structure is subsequently broken in one direction to form rods and in a second direction (at right angles to the first direction) to form individual multilayer capacitor elements. These elements are, in succession, calcined and sintered (maximum temperature 1180-1220 °C) in air.
Finally, the multilayer capacitor elements are provided, on two facing surfaces, with electric connections of copper by means of immersion copperplating. These connections are galvanically reinforced and provided with a solderable NiSn alloy. Subsequently, the mechanical and electrical properties of the resultant ceramic multilayer capacitors can be measured.
By means of the method described hereinbefore, a first number of ceramic multilayer capacitors (b series) was manufactured on the basis of the above-mentioned doped BaTiO3. The Ag-Pd screen-printing paste used in said b-series did not contain copper oxide. In addition, a second number of ceramic multilayer capacitors (a-series) was manufactured. The screen-printing paste used for said second series contained approximately 5 wt. % copper oxide, calculated with respect to the overall quantity of Ag, Pd and copper oxide. Both series were tested for mechanical strength and service life.
Visual inspection (light microscopy) of slices of both series revealed that the capacitors of the a-series exhibited considerably fewer cracks than the capacitors of the b- series after they had been exposed to a thermal treatment (for 10 seconds at 330 °C). The percentage of rejects as a result of cracks was 30% lower in the a-series than in the b-series.
The graph shown in Fig. 2 shows the results of accelerated life tests (140 °C, 400 V, DC) for maximally 100 hours. In the graph, the resistance R (ohm) is plotted as a function of time T (hours), the time scale exhibiting a logarithmic variation. Fig. 2 shows that the inventive capacitors of the a-series have a much longer service life than the capacitors of the b-series. Besides, it has been found that the reproducibility of the resistance value of the capacitors of the a-series is also much higher than that of the capacitors of the b- series.
The above description shows that the presence of a relatively small, yet effective quantity of copper oxide in the electrode material Pd or of of Pd-Ag leads to a considerable increase of the internal mechanical strength and of the service life of CMCs. By employing the present invention, the number of rejects in the manufacture of capacitors can be reduced considerably.
Claims
1. A ceramic multilayer capacitor comprising a number of ceramic layers on the basis of barium titanate as well as a number of electrode layers of palladium or of a silver-palladium alloy, the ceramic layers and the electrode layers being alternately stacked to form a multilayer, which is also provided with two external electric connections which are in contact with a number of said electrode layers, characterized in that the electrode layers comprise copper oxide.
2. A ceramic multilayer capacitor as claimed in Claim 1, characterized in that the quantity of copper oxide in the palladium or the silver-palladium alloy of the electrode layers ranges from 0.5 to 15 wt. %, calculated with respect to the overall quantity of palladium, silver and copper oxide.
3. A ceramic multilayer capacitor as claimed in Claim 1 or 2, characterized in that the thickness of the electrode layers ranges between 0.7 micron and 2.0 microns.
4. A ceramic multilayer capacitor as claimed in any one of the preceding Claims, characterized in that the composition of the main phase of the material of the ceramic layers corresponds to the formula
[Bag 25Sr0 02Cao 05Nd0 30Gd0 2oXo.i8]rTiι.ooo]03, wherein X indicates the number of vacancies in the Ba sites.
5. A method of manufacturing a ceramic multilayer capacitor, which method comprises the following steps: - screen-printing of electrode layers on a ceramic foil using a palladium or a silver-palladium paste, stacking a number of these foils to form a multilayer, compressing the multilayer, subdividing the multilayer into individual multilayer elements, - calcining and sintering of the multilayer elements, providing electric connections at one or more side faces of the multilayer elements, characterized in that the palladium or the silver-palladium paste contains copper oxide, and sintering is carried out at a maximum temperature in the range between 1180 and 1220 °C.
6. A method of manufacturing a ceramic multilayer capacitor as claimed in Claim 5, characterized in that the palladium or the silver-palladium paste contains a quantity of copper oxide in the range from 0.5 to 15 wt. %, calculated with respect to the overall quantity of palladium, silver and copper oxide.
7. A method of manufacturing a ceramic multilayer capacitor as claimed in Claim 5 or 6, characterized in that the thickness of the electrode layers ranges from 0.7 to 2.0 microns.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP97943117A EP0885446A1 (en) | 1996-12-06 | 1997-10-20 | Multilayer capacitor |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP96203453 | 1996-12-06 | ||
EP96203453 | 1996-12-06 | ||
EP97943117A EP0885446A1 (en) | 1996-12-06 | 1997-10-20 | Multilayer capacitor |
PCT/IB1997/001312 WO1998025281A1 (en) | 1996-12-06 | 1997-10-20 | Multilayer capacitor |
Publications (1)
Publication Number | Publication Date |
---|---|
EP0885446A1 true EP0885446A1 (en) | 1998-12-23 |
Family
ID=8224667
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP97943117A Withdrawn EP0885446A1 (en) | 1996-12-06 | 1997-10-20 | Multilayer capacitor |
Country Status (5)
Country | Link |
---|---|
US (1) | US6128177A (en) |
EP (1) | EP0885446A1 (en) |
JP (1) | JP2000504502A (en) |
TW (1) | TW327690B (en) |
WO (1) | WO1998025281A1 (en) |
Families Citing this family (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH11340075A (en) * | 1998-05-27 | 1999-12-10 | Philips Japan Ltd | Dielectric cermic composition |
JP2001035738A (en) * | 1999-07-15 | 2001-02-09 | Murata Mfg Co Ltd | Laminated ceramic electronic component |
JP3596743B2 (en) * | 1999-08-19 | 2004-12-02 | 株式会社村田製作所 | Manufacturing method of multilayer ceramic electronic component and multilayer ceramic electronic component |
US6517931B1 (en) * | 2001-10-15 | 2003-02-11 | Ferro Corporation | Silver ink for forming electrodes |
JP4305808B2 (en) * | 2002-07-03 | 2009-07-29 | 太陽誘電株式会社 | Multilayer capacitor |
KR20050019214A (en) * | 2003-08-18 | 2005-03-03 | 한국과학기술원 | Polymer/ceramic composite paste for embedded capacitor and method for fabricating capacitor using the same |
JP2006041393A (en) * | 2004-07-29 | 2006-02-09 | Tdk Corp | Multilayer ceramic capacitor |
KR101079408B1 (en) * | 2009-12-24 | 2011-11-02 | 삼성전기주식회사 | multilayer ceramic capacitor and fabricating method of the same |
TWI656445B (en) * | 2017-05-26 | 2019-04-11 | 慧榮科技股份有限公司 | Methods for scheduling and executing commands in a flash memory and apparatuses using the same |
Family Cites Families (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3763409A (en) * | 1972-04-20 | 1973-10-02 | Du Pont | Capacitor with copper containing electrode |
US3851228A (en) * | 1972-04-20 | 1974-11-26 | Du Pont | Capacitor with copper oxide containing electrode |
US3798516A (en) * | 1973-01-17 | 1974-03-19 | Du Pont | Ceramic capacitors with noble electrodes alloy |
US4241378A (en) * | 1978-06-12 | 1980-12-23 | Erie Technological Products, Inc. | Base metal electrode capacitor and method of making the same |
GB8518945D0 (en) * | 1985-07-26 | 1985-09-04 | Ngk Insulators Ltd | Forming copper film on ceramic body |
US4882651A (en) * | 1988-12-05 | 1989-11-21 | Sprague Electric Company | Monolithic compound-ceramic capacitor |
US5126318A (en) * | 1991-03-13 | 1992-06-30 | Westinghouse Electric Corp. | Sputtering method for forming superconductive films using water vapor addition |
DE4334454A1 (en) * | 1993-10-09 | 1995-04-13 | Philips Patentverwaltung | Substituted barium-neodyn-titanium perovskite Dielectric, ceramic composition, capacitor and microwave component |
EP0739019B1 (en) * | 1994-10-19 | 2003-12-03 | TDK Corporation | Multilayer ceramic chip capacitor |
-
1997
- 1997-05-24 TW TW086107027A patent/TW327690B/en active
- 1997-10-20 WO PCT/IB1997/001312 patent/WO1998025281A1/en not_active Application Discontinuation
- 1997-10-20 EP EP97943117A patent/EP0885446A1/en not_active Withdrawn
- 1997-10-20 JP JP10525381A patent/JP2000504502A/en active Pending
- 1997-12-02 US US08/982,797 patent/US6128177A/en not_active Expired - Fee Related
Non-Patent Citations (1)
Title |
---|
See references of WO9825281A1 * |
Also Published As
Publication number | Publication date |
---|---|
US6128177A (en) | 2000-10-03 |
TW327690B (en) | 1998-03-01 |
JP2000504502A (en) | 2000-04-11 |
WO1998025281A1 (en) | 1998-06-11 |
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